In aircraft engine manufacturing it is often a requirement to determine the total thrust generated by an engine at various airspeeds. In a conventional turboprop engine, the thrust was sometimes determined by measuring the torque generated at the propeller shaft utilizing a dynamometer or the like, and then solving for thrust.
In the next generation of commercial airline aircraft, consideration is being given to powering these aircraft by means of an unducted bladed turbofan engine. This engine includes a forward compressor section, an intermediate burner section, a high pressure turbine section, a rear propeller/power turbine section and an exhaust section. The propeller or fan section is made up of a number of counterrotating blades which propel the aircraft and which are mounted on internal power turbines which are driven by the exhaust gases from the high pressure turbine section. After driving the turbines, the exhaust gases are discharged from the exhaust section of the engine to produce additional thrust.
Unlike conventional turboprop engines, in the unducted turbofan engine there is no propeller shaft upon which to conveniently attach a dynamometer to accurately measure the torque generated, and in turn to calculate thrust.
A number of conventional apparatus for measuring torque have been disclosed. For example, in U.S. Pat. No. 4,176,547 by McClure et al, there is disclosed a ring assembly which is used as part of a test stand for measuring the performance of a turboshaft engine wherein one of the rings is rigidly attached to the test stand and the other ring is rigidly attached to the outer casing of the engine. When the engine is operating, reaction torque between the rings is measured by a number of strain gauge beams which interconnect the two rings.
Other torque measuring apparatus include U.S. Pat. No. 3,190,113 Lucia, which pertains to a measuring device which is attached to a prime mover and which has a flywheel which is accelerated from a first known angular velocity to a second known angular velocity over measured time, the torque being a function of the measured time and the moment of inertia of the flywheel.
In Richmond, U.S. Pat. No. 3,190,113, there is disclosed torque measuring apparatus which measures the magnitude and frequency of radial deflection of a selected point on an outer ring gear of a gearbox due to torque generated by the various gears in the gearbox which are operatively connected to the outer ring gear.
Furthermore, in U.S. Pat. No. 2,129,241 by Sarazin there is a torque measuring device which is mounted to a shaft and which measures shaft torque as a function of the shaft velocity and the angle of centrifugal displacement of a pair of pivotally mounted arms.
Eckart, in U.S. Pat. No. 3,788,130 discloses a torque measuring device that measures the reaction force on one of a pair of intermeshing helical gears of an engine gearbox so as to determine the engine torque output.
Other devices for measuring engine parameters are disclosed in U.S. Pat. No. 4,417,469 by Stevenson et al which includes apparatus for determining the speed of an engine and for determining the phase shift between a timing shaft and a fuel cam shaft of the engine, by generating signals as a function of the respective shaft angular velocities.
Apparatus for measuring thrust from a rocket engine is disclosed in U.S. Pat. No. 3,788,130 by Ormond wherein the rocket engine is supported in a nose down vertical manner on a base plate which rests on a number of load cells for measuring the thrust force when the engine is operating.
Another torque measuring device is disclosed by Stratton in U.S. Pat. No. 3,403,546, in which variations in the concrete mix contents of a rotating mixer are determined by measuring the variations in load torque delivered by an engine to the mixer via a drive chain.
Another patent pertaining to cement mixers is U.S. Pat. No. 1,980,184 by Butcher where there is disclosed a system for recording the power output to rotate a drum of a cement mixer wherein the recording apparatus is geared to the rotating drum by means of an outer perimeter gear on the drum.
Finally, in U.S. Pat. No. 4,083,235 by Gallant there is disclosed a compressor stall warning system for a gas turbine engine in which turbine inlet temperature and compressor rotor speed are measured and their ratios calculated to generate a signal when the ratio exceeds a predetermined limit.